Microstructuring of an optical waveguide for producing functional optical elements

ABSTRACT

The invention relates to a method for microstructuring an optical waveguide having a first cross-sectional region with a first refractive index, a second cross-sectional region with a second refractive index, and a boundary region in the transition from the first to the second cross-sectional region, in which the optical waveguide is exposed to laser radiation in the form of at least one ultra-short single pulse or a sequence of pulses with a defined energy input, whereby the radiant exposure takes place in such a manner that a modification of at least one optical property of the optical waveguide takes place at at least one defined portion of the boundary region.

The invention relates to a method for microstructuring an opticalwaveguide with a first cross-sectional region having a first refractiveindex, a second cross-sectional region having a second refractive indexand a boundary region in the transition from the first to the secondcross-sectional region, in which the optical waveguide is exposed tolaser radiation in the form of at least one ultra-short single pulse ora sequence of pulses with defined energy input. The invention alsorelates to an optical functional element having an optical waveguide.The invention also relates to a device for microstructuring an opticalwaveguide with laser radiation.

A method of the type mentioned at the beginning is known from DE 197 39456. In accordance with it, a modification is produced in a core of anoptical waveguide with a single pulse or a sequence of pulses having adefined number of pulses. The optical waveguide core is surrounded by anoptical waveguide cladding, the material of which has a lower refractiveindex than that of the optical waveguide core. The pulse intensity ischosen so that the destruction threshold is exceeded with each singlepulse. By a micro-explosion in the material, scattering centres areproduced, which effect a scattering of a part of the radiation guided inthe optical waveguide core in all directions. From the article PhysicalReview Letters, Vol. 74 (1995), pages 2248 to 2251 is known the use oflaser pulses having a duration of a few 10 ns down into thesub-picosecond range for material changes in the micrometer range byvirtue of the low energy.

The production of grating structures in an optical waveguide is knownfrom U.S. Pat. No. 6,384,988. The optical waveguide consists of aphotosensitive material, which is illuminated according to the gratingstructure.

The last-named method has the disadvantage that it can only be used withphotosensitive optical waveguide materials. The other mentioned methodsfrom the prior art do not enable any controlled coupling of light out ofthe optical waveguide or coupling of light into the optical waveguide.The method of DE 107 39 456 only allows the scattering of light from theoptical waveguide in all directions.

The object of the invention is to provide a method for themicrostructuring of an optical waveguide of the type mentioned at thebeginning which does not have the mentioned disadvantages. Anotherobject of the invention is to provide an optical functional element withan optical waveguide, which enables a (particularlydirectional-selective) coupling of light out of an optical waveguide orcoupling of light into an optical waveguide. Another object of theinvention is to provide a device for the microstructuring of an opticalwaveguide with laser radiation, which enables the manufacture of opticalfunctional elements with the mentioned properties.

In accordance with a first aspect of the invention, the object isachieved by a method for the microstructuring of an optical waveguidewith a first cross-sectional region having a first refractive index, asecond cross-sectional region having a second refractive index, and aboundary region in the transition from the first to the secondcross-sectional region, in which the optical waveguide is exposed tolaser radiation in the form of at least one ultra-short single pulse ora single pulse with a defined energy input, whereby the radiation takesplace in such a manner that a modification of at least one opticalproperty of the optical waveguide occurs at one defined portion at leastof the boundary region.

The method according to the invention is distinguished by the fact thatthe optical waveguide is modified not in the interior of across-sectional region, such as, for example, the core of the opticalwaveguide, but in defined manner in the boundary region between thefirst and the second cross-sectional region, i.e. for example at theboundary surface between the optical waveguide core and the opticalwaveguide cladding. The first cross-sectional region may thus be, forexample, an optical waveguide core with a refractive index n₁ and thesecond cross-sectional region may be an optical waveguide cladding witha refractive index n₂<n₁. In this case radiation takes place in such amanner that a modification of at least one optical property of theoptical waveguide occurs at one defined portion at least of the boundaryregion.

A permanent change in a value of an optical parameter of the opticalwaveguide is understood as a change in an optical property of theoptical waveguide. Such an optical parameter is, for example, therefractive index of the material of the first or second cross-sectionalregion. With a change in the refractive index in the boundary regionbetween the first and the second cross-sectional region, the reflectionof a light beam guided in the first cross-sectional region can beinfluenced in a purposeful manner at the boundary surface to the secondcross-sectional region. This may occur, for example, in such a mannerthat instead of total reflection of the light conveyed in the firstcross-sectional region, only a reflection of a part of the lightintensity striking the boundary region occurs. This results in that apart of the light conveyed in the first cross-sectional region iscoupled out of said region. Depending on the arrangement andconstruction of the modified portion of the boundary region, irradiationin a specific direction and in a determined intensity ratio to the lightintensity conveyed in the optical waveguide can be achieved thereby.

With the method according to the invention, an optical waveguide isstructured on a micro-optical scale, which has a first cross-sectionalregion with a first refractive index, a second cross-sectional regionwith a second refractive index and a boundary region in the transitionfrom the first to the second cross-sectional region. The boundary regionin the transition from the first to the second cross-sectional regionforms a boundary surface in the ideal case. However, it is obvious thata boundary surface can only be modified by the boundary region aroundthe boundary surface being modified. This means that a portion of thefirst cross-sectional region close to the boundary surface or a portionof the second cross-sectional region close to the boundary surface orrespectively a portion in both cross-sectional regions close to theboundary surface is modified.

However, the method according to the invention is not suitable just foruse in the microstructuring of an optical waveguide with a step-shapedrefractive index profile. It may also be used with an optical waveguidehaving a continuous cross-sectional profile of the refractive index. Theboundary region in which a modification of at least one optical propertyof the optical waveguide is produced is in this case a preselectableregion in a depth portion of the optical waveguide. In this case themodifications thus lie beneath the surface in the optical waveguide witha gradient index profile.

In a preferred embodiment of the invention, the modification of at leastone optical property of the optical waveguide lies in the creation of ascattering centre by micro-damage or by removal of material in theboundary region. Removal of material may take place by amicro-explosion, for example.

In another preferred embodiment of the method according to theinvention, the modification is a transformation of the phase of thematerial of the first cross-sectional region or of the material of thesecond cross-sectional region or of the phase of both cross-sectionalregions.

The controlled production of a modification in accordance with theabove-mentioned embodiments, i.e. change in refractive index, productionof a scattering centre by micro-damage or phase transformation, takesplace in a preferred exemplified embodiment of the method in which thelaser radiation is chosen in such a manner that, at the defined portionof the boundary region provided for the modification, a charge carrierplasma is produced, for example an electron plasma, with a chargecarrier density depending on the desired modification is produced.

Since the energy transfer out of the laser beam into the material andthus the material reaction or material modification is dependent on theinduced plasma, the use of suitable laser pulses is necessary to controlthe plasma density. The interaction between the laser radiation and thematerial for the manufacture of optical waveguides greatly depends onthe ratio of the energy density to the selected power density of therespective laser radiation. Only the use of time-modulated laserradiation increases the ratio between the power density and the energydensity of a laser pulse (also called “single pulse”. To achieve themodifications provided in accordance with the invention in the boundaryregion, it is necessary to work with high power density with a lowenergy density and thus to create the condition for controlling theplasma density.

The high power density of the laser beam that can be achieved withultra-short laser pulses induces non-linear optical effects of theexcitation at the defined site in the boundary region or in the interiorof the material, so that a very local energy effect takes place in theotherwise transparent material. Changes in the optical properties, whichare also known as modifications, may thus be achieved at the definedsite depending on the material combination and the power density.

The laser radiation therefore preferably has a power density of roughly10¹⁰ W/cm² or of more than 10¹⁰ W/cm². In this power density range anefficient coupling-in of the laser energy is predominantly produced vianon-linear optical effects, such as multiphoton absorption, tunnel andcascade ionisation.

The mentioned power density may be achieved with appropriate focusing ofthe laser radiation with laser pulses having a duration of 10⁻¹⁰ secondsand an energy of roughly 10 nanojoules (nj) or less than 10 nj. Thepulse length is chosen according to the desired plasma density. Thelaser pulse durations used are preferably between 0.1 and 50picoseconds.

In this case the wavelength of the laser radiation is preferably chosenso that the optical waveguide in the light path to the defined portionof the boundary region is transparent or partially transparent for lightof the chosen wavelength up to a power density critical for the controlof the plasma density, thus for example the mentioned power density ofroughly 10¹⁰ W/cm². The component consequently remains transparent onthe light path until the laser radiation reaches a power density in thementioned range by virtue of the increasing focusing.

The choice of the light wavelength is consequently also dependent on therespective material of the cross-sectional regions penetrated byradiation.

The focusing of the laser beam onto the defined portion of the boundaryregion preferably takes place by using a microscope lens.

In a preferred refinement of the method, a laser beam is directed sothat it enters the optical waveguide at an angle of 90° to an outer faceof the optical waveguide at the point of impact. However, otherembodiments of the laser beam guidance are also possible. The laser beamcan also enter the optical waveguide at another angle. Instead of amicroscope lens or in addition thereto, focusing of the laser beam mayalso be achieved with a mirror lens system in the defined portion of theboundary region. It just depends on power density which is sufficient tocontrol the plasma density at the defined portion of the boundaryregion.

In another preferred embodiment of the invention, a laser beam isconveyed through an immersion fluid before it enters the opticalwaveguide.

In another preferred embodiment of the invention, the laser beam ismoved relative to the optical waveguide or the optical waveguide ismoved relative to the laser beam. Thus more complicated modificationstructures can also be achieved by machine production. The opticalwaveguide may, for example, be rotated relative to the laser beam and/ordisplaced in its longitudinal direction. In this manner modificationscan be performed at any point of the boundary region in any form bothonly as a change in the refractive index and also in the form of solidscattering centres and also in the form of phase transformations or as acombination of two or all three mentioned modifications.

In an optical waveguide which has, seen in cross section from theinterior outwards, more than two cross-sectional portions with differentrefractive indices and accordingly also several boundary regions ofadjacent cross-sectional portions, modifications at more than oneboundary region may be provided by corresponding variations in thefocusing.

The same applies for an optical waveguide having a continuouscross-sectional profile of the refractive index. Here too, modificationsin several previously selected cross-sectional portions may take placeby different focusing. It is obvious that, with such a gradient indexfibre, these cross-sectional regions correspond to the boundary regionof the embodiments of the invention which produce modifications in anoptical waveguide having a step-shaped refractive index profile.

Optical functional elements can be manufactured with themicrostructuring method according to the invention. The arrangement andstructure of the modifications depends on the desired functionalelement.

Thus in one embodiment of the invention it is provided that themodifications be circumferentially disposed, so that with a coupling-outelement a defined irradiation takes place in the radial direction in adefined lengthwise portion of the optical waveguide. This may beprovided, for example, in a scattered light applicator, as is used inmedical engineering for the introduction of laser light into tissue.

Another embodiment provides introducing the modifications in the opticalwaveguide in a defined selected manner at an extremely limited position,so that irradiation only takes place in one direction, or so that thissite may serve as an inward coupling element. Other possible embodimentsof the modifications at the fibre core/fibre cladding boundary face arelines, curves and surfaces at a defined angle and lengths, as well ascombinations of these embodiments.

According to a second aspect of the invention, the achievement of theabove-mentioned object lies in an optical functional element having anoptical waveguide, which has a first cross-sectional region with a firstrefractive index, a second cross-sectional region with a secondrefractive index, and a boundary region in the transition from the firstto the second cross-sectional region, wherein at least a defined portionof the boundary region is provided with a modification at least of oneoptical property of the optical waveguide.

The optical functional element according to the invention isdistinguished by the fact that the modification is provided in aboundary region in the transition from the first to the secondcross-sectional region. In this manner, the coupling of laser radiationinto the optical waveguide or the coupling of laser radiation out of theoptical waveguide or both are locally influenced with microscopicprecision. The directional dependency of the inward or outward couplingof laser radiation can be influenced in a purposeful manner by anappropriate choice of the modification of the optical properties in theboundary region. In another exemplified embodiment of the opticalfunctional element according to the invention, a modification on aplurality of defined portions of the boundary region is provided in sucha manner that of the modified boundary region portions a radialirradiation of defined, uniform light intensity takes place if light iscoupled into the optical waveguide at one longitudinal end.

In another exemplified embodiment of the optical functional element ofthe invention, the modification is disposed at a plurality of definedportions of the boundary region in the longitudinal direction of thewaveguide or in a direction perpendicular thereto or in both mentioneddirections of the optical waveguide in such a manner that an opticalgrating, a spiral, a cross, a photonic bandgap structure, a combinationof lines and dots, or a combination of the above-mentioned structures isprovided.

The optical waveguide can contain, for example, materials such asquartz, glass, glass ceramics, one or more plastics, fluorides, orsimilar transparent materials, or combinations of materials.

In accordance with a third aspect of the invention, the object isachieved by a device for microstructuring an optical waveguide withlaser radiation, wherein a laser constructed to emit at least one lightpulse and a focussing device are provided in such a manner that laserradiation having a power density of roughly 10¹⁰ W/cm2 or of more than10¹⁰ W/cm 2 can enter a presettable depth portion of an opticalwaveguide.

In a preferred embodiment of the device, in accordance with the thirdaspect of the invention the laser is constructed to emit light pulseswith a duration of max. 10⁻¹⁰ seconds, preferably 0.1 to 50 ps. Inanother embodiment of the invention, the laser is constructed to emitlight pulses having an energy of roughly 10 nj or less than 10 nj. Inanother embodiment of the invention, the frequency of the laserradiation is chosen to correspond to the material of the opticalwaveguide on the light path penetrated by radiation in the opticalwaveguide so that laser radiation with a power density of roughly 10¹⁰W/cm² or of more than 10¹⁰ W/cm² can only enter the defined depthportion.

In another embodiment of the invention, a mounting for an opticalwaveguide is provided, which is constructed to hold the opticalwaveguide so that it is displaceable in its longitudinal direction orcan rotate around its longitudinal axis, or both. In another embodimentof the invention, the focussing device is mounted for the performance ofone or more of the following movements: a displacement in the directionof the spacing of the optical waveguide or in the longitudinal directionof the optical waveguide, or a rotation around its longitudinal axis.

The invention is described in further detail below with reference to thedrawings by means of exemplified embodiments. Therein:

FIG. 1 shows a schematic representation of a device for microstructuringan optical waveguide,

FIG. 2 shows a microscope photo of a quartz glass fibre modified by themethod according to the invention,

FIG. 3 shows a photo of modified regions of a quartz glass fibre, intothe longitudinal side of which light is coupled,

FIG. 4 shows a diagram of the radiated power of the fibres from FIG. 2in relationship to the power coupled into the fibre as a function of theplace of modification.

FIG. 1 shows an exemplified embodiment of a device for themicrostructuring of an optical waveguide. FIG. 1 is a schematic diagram.A laser L emits a laser beam. The laser beam is represented by marginalbeams R1 and R2 and also by an arrow 1, which shows the beam direction.The laser beam is directed to an optical waveguide LWL by means of amicroscope lens 2. In the present exemplified embodiment the opticalwaveguide comprises an optical waveguide cladding 3 and an opticalwaveguide core 4. The cladding 3 is constructed from a material having alower refractive index than the core 4. In the transition from thecladding 3 to the core 4 there is a boundary region 7, which here isalso called a boundary surface.

The distance between the microscope lens 2 and the optical waveguide LWLis adjustable, which is symbolised by the double arrow 5. The opticalwaveguide LWL is rotatably mounted around its longitudinal axis, whichis symbolised by the double arrow 6. The microscope lens 2 isdisplaceable in the longitudinal direction of the optical waveguide.

By varying the distance of the microscope lens 2 from the boundarysurface 7, the desired intensity and the most advantageous region in thetransition between the optical waveguide core and the optical waveguidecladding can be set. Depending on the desired modification, apart fromthe focusing, the intensity of the laser beam can also be appropriatelyadjusted. For example, attenuation elements such as neutral grey filtercan be used.

By a rotation 6 of the optical waveguide LWL, the modification can beproduced with an extension in the circumferential direction of theoptical waveguide LWL. Such a modification is also known as a radialmodification. By displacing the microscope lens, a modification can beproduced with an extension in the longitudinal direction of the opticalwaveguide LWL.

FIG. 2 shows an exemplified embodiment of an optical waveguide 10 in amicroscope photo. The optical waveguide 10 is a quartz glass fibrehaving a core with a diameter of 600 micrometres and a cladding with adiameter of 660 micrometers. The longitudinal direction of the opticalwaveguide 10 extends from the left-hand side to the right-hand side ofthe image in FIG. 2. For the represented photo the optical waveguide waspenetrated by radiation transversely to the longitudinal direction.Transverse strips of different brightness in the picture that extendfrom the left-hand to the right-hand edge are primarily attributed tothe radiation.

Vertical, dark stripes regularly spaced in the longitudinal direction ofthe fibre can be seen between an upper fibre edge 12 and a lower fibreedge 14. These stripes are modifications. In the transmitted light ofthe microscope they appear darker than the non-modified longitudinalportions of the fibre. Modifications 16 and 18 are marked as examples.

To produce the modifications, laser pulses of a wavelength of 800 nm, apulse duration of 0.2 picoseconds, a single pulse energy of 2.3 μJ and arepetition rate of 1 kHz were used. The modifications were performed todifferent depths by the displacement of the microscope lens (40×,NA=0.63) in the direction of the fibre core. The greater depth of themodifications on the right-hand side of the picture can be seen, forexample, at modification 18, which appears blurred in the photo in FIG.3. However, modification 16, which was in the focus of the microscopeduring the photograph, appears sharp.

FIG. 3 shows another exemplified embodiment of a quartz glass fibre 20having laser-induced modifications. The quartz glass fibre 20 also has acore of 600 micrometers diameter and a cladding of 660 micrometresdiameter. Here modifications were achieved with the aid of laser pulseshaving a basic wavelength of 800 nm, a pulse duration of 3 picosecondsand a single pulse energy of 3.8 μJ. The modifications took place with aspacing in the longitudinal direction of 10 micrometres over the entirecircumference of the fibre 20.

The photo of FIG. 3 shows the radiation of light from the modifiedregions of the quartz glass fibres. For this a helium-neon laser iscoupled in at the end of the fibre. Modified regions 22, 24 and 26,which are disposed one behind the other in the longitudinal direction ofthe fibre, can be clearly seen. A short portion 28 with a small numberof modifications is disposed between the modified regions 22 and 24.Another short portion 30 with a smaller number of modifications isdisposed between the portions 24 and 26. The regions 28 and 30 can berecognised from the fact that lesser radiation takes place from them andthey therefore appear darker in FIG. 3. Dark portions 32 and 34, inwhich the fibre was not modified, can be seen at the left-hand andright-hand edge respectively in the extension of the modified regions.

FIG. 4 shows a diagram in which the entire radiated power of the fibre20 from FIG. 3 in relation to the power of the laser beam of thehelium-neon laser which is coupled into the fibre is represented on theordinate (Y axis). The distance in the longitudinal direction of themeasurement point from one longitudinal end of the modified region ofthe fibre is entered on the abscissa (X axis). The radiation begins inthe radial direction coming from great distances (corresponding to thedirection of propagation of the laser beam in the fibre) at a distanceof 10 mm and reaches a maximum with a distance of roughly 7 mm. Towardslow spacing values, the radially radiated intensity decreases and hasreached a relative intensity of only 10% at the end of the modificationregion. This is attributed to the fact that the radiation in themodified regions, which lie closer to the helium-neon laser, is so highthat a considerable part of the radiated power is coupled out of thefibre by virtue of the radial radiation in these regions. With a greaterdistance of the helium-neon laser, the relative intensity of theoutwardly coupled laser light therefore also necessarily drops.

1. A method for the microstructuring of an optical waveguide comprisingthe steps of: providing an optical waveguide comprising a firstcross-sectional region having a first refractive index, a secondcross-sectional area having a second refractive index, and a boundaryregion in the transition from the first to the second cross-sectionalarea, exposing the optical waveguide to laser radiation in the form ofat least an ultra-short single pulse or a sequence of pulses with adefined energy input; and modifying at least one optical property of theoptical waveguide at one defined portion at least of the boundary regionas a result of the step of exposing the optical waveguide to laserradiation.
 2. The method according to claim 1, in which the modificationis a change in the refractive index of the material of the first or ofthe second cross-sectional region or both.
 3. The method according toclaim 1, in which the modification is the creation of a scatteringcenter by microdamage or by the removal of material.
 4. The methodaccording to claim 1, in which the modification is a transformation ofthe phase of the material of the first or of the second cross-sectionalregion.
 5. The method according to claim 1, in which the laser radiationis chosen in such a manner that at the defined portion of the boundaryregion a charge carrier plasma with a charge carrier density dependenton the desired modification is produced.
 6. The method according toclaim 5, in which the laser radiation comprises a power density ofroughly 10¹⁰ W/cm² or of more than 10¹⁰ W/cm².
 7. The method accordingto claim 6, in which the laser radiation comprises single pulses havinga duration of roughly 10⁻¹⁰ seconds or of between 0.1 ps and 50 ps andan energy of roughly 10 nanojoules (nj) or less than 10 nanojoules (nj).8. The method according to claim 6, in which the wavelength of the laserradiation is chosen so that the optical waveguide is transparent in thelight path up to the defined portion of the boundary region for light ofthe chosen wavelength up to a power density of roughly 10¹⁰ W/cm². 9.The method according to claim 1, in which a laser beam is focused ontothe defined portion of the boundary region by means of a microscopelens.
 10. The method according to claim 1, in which a laser beam isirradiated so that it enters the optical waveguide at an angle of 90° toan outer face of said optical waveguide at the point of impact.
 11. Themethod according to claim 1, in which a laser beam is guided through animmersion fluid before it enters into the optical waveguide.
 12. Themethod according to claim 1, in which the modification is produced insuch a manner that at the respective portion of the boundary regionlight can be coupled out of the waveguide or in such a manner that lightcan be coupled into the waveguide at the respective portion of theboundary region, or that light can be coupled in and also coupled out atthe respective portion of the boundary region.
 13. The method accordingto claim 1, in which the modification is produced on a plurality ofdefined portions of the boundary region in such a manner that from themodified boundary region portions a radial radiation of defined, uniformlight intensity takes place when light is coupled into the opticalwaveguide at one longitudinal end.
 14. The method according to claim 1,in which the modification is produced at a plurality of defined portionsof the boundary region in the longitudinal direction of the opticalwaveguide or in a direction perpendicular thereto or in both mentioneddirections of the optical waveguide in such a manner that an opticalgrating, a spiral, a cross, a photonic bandgap structure, a combinationof lines and dots, or a combination of the above-mentioned structures isproduced.
 15. The method according to claim 1, in which the opticalwaveguide is moved relative to the laser beam or the laser beam is movedrelative to the optical waveguide.
 16. The method according to claim 1,in which the first cross-sectional portion is an optical waveguide coreand the second cross-sectional portion is an optical waveguide cladding.17. The method according to claim 1, in which the optical waveguidecomprises from the inside to the outside more than two cross-sectionalportions having different refractive indices and a corresponding numberof boundary regions of adjacent cross-sectional portions, and in whichmodifications are disposed at more than one boundary region.
 18. Themethod according to claim 1, in which the optical waveguide comprises acontinuous cross-sectional profile of the refractive index, and in whichthe modification takes place in at least one pre-selectedcross-sectional portion.
 19. (canceled)
 20. An optical functionalelement comprising: an optical waveguide comprising a firstcross-sectional region with first refractive index, a secondcross-sectional region with a second refractive index, and a boundaryregion in the transition from the first to the second cross-sectionalregion, wherein at least one defined portion of the boundary region isprovided with a modification of at least one optical property of theoptical waveguide.
 21. The optical functional element according to claim20, in which the modification is a change in the refractive index of thematerial of the first or second cross-sectional region or of both. 22.The optical functional element according to claim 20, in which themodification is the creation of a scattering centre by micro-damage orby the removal of material.
 23. The optical functional element accordingto claim 20, in which the modification is a transformation of the phaseof the material of the first or of the second cross-sectional region orof both.
 24. The optical functional element according to claim 20, inwhich the modification is constructed in such a manner that at therespective portion of the boundary region light is coupled out of thewaveguide, or in such a manner that light at the respective portion ofthe boundary portion can be coupled into the waveguide, or in such amanner that light can be coupled in and also coupled out at therespective portion of the boundary region.
 25. The optical functionalelement according to claim 20, in which the modification is provided ata plurality of defined portions of the boundary region in such a mannerthat from the modified boundary region portions a radial radiation ofdefined, uniform light intensity takes place if light is coupled intothe optical waveguide at a longitudinal end.
 26. The optical functionelement according to claim 20, in which the modification is disposed ata plurality of defined portions of the boundary region in thelongitudinal direction of the optical waveguide or in a directionperpendicular thereto or both mentioned directions of the opticalwaveguide in such a manner that an optical grating, a spiral, a cross, aphotonic bandgap structure, a combination of liens and dots, or acombination of the above-mentioned structures is produced.
 27. A devicefor microstructuring an optical waveguide with laser radiation, thedevice comprising: a laser constructed to emit at least one light pulse,and a focusing device, wherein the laser radiation has a power densityof roughly 10¹⁰ W/cm² or more.
 28. The device according to claim 27, inwhich the laser is constructed to emit light pulses with a maximumduration of roughly 10⁻¹⁰ seconds or of between 0.1 and 50 ps.
 29. Thedevice according to claim 28, in which the laser is constructed to emitlight pulses having an energy of roughly 10 nanojoules (nj) or less than10 nanojoules (nj).
 30. The device according to claim 27, in which thefrequency of the laser radiation is chosen to correspond to the materialof the optical waveguide on the light path penetrated by radiation inthe optical waveguide, so that laser radiation with a power density ofroughly 10¹⁰ W/cm² or of more than 10¹⁰ W/cm² can only enter the defineddepth portion.
 31. The device according to claim 27, having a mountingfor an optical waveguide, which is constructed to hold the opticalwaveguide so that it is displaceable in its longitudinal direction orcan rotate around its longitudinal axis, or both.
 32. The deviceaccording to claim 27, in which the focusing device is a microscopelens.
 33. The device according to claim 27, in which the focusing devicefor performing one or more of the following movements is mounted: adisplacement in the direction of the spacing of the optical waveguide orin the longitudinal direction of the optical waveguide, or a rotationaround its longitudinal axis.
 34. The device according to claim 27, inwhich the optical waveguide and the focusing device are disposed in sucha manner that a laser beam enters the optical waveguide at an angle of90° to an outer face of said optical waveguide at the point of impact.